This invention relates generally to temperature measurment and more particularly to instruments including improved thermocouple transducer apparatus.
At the current state of the art when it is desired to measure temperatures below approximately 300 degrees fahrenheit (149 degrees celsius) there are very accurate and conveniently linear temperature-voltage transducers available. These generally utilize semiconductor devices with associated sophisticated electronic circuitry. However, above such temperatures, the limitations of these transducers significantly compromise their accuracy, reliability, or longevity; and the practicioner must generally choose between three other types of transducers:infrared sensors, resistance temperature detectors, or thermocouples.
Infrared sensors are expensive, complex, bulky, and require special skills in their effective operation. Resistance temperature detectors, for high temperatures, generally require a relatively large amount of expensive platinum. The mass of the platinum is very costly and inherently has a great deal of thermal inertia, thus limiting its response speed and effective sensitivity.
The thermocouple option utilizes the phenomenon of joining dissimilar metals and generating at the junction an electromotive force which is a reliable function of its temperature. Difficulties in the past included 1. the need for maintaining the "reference" junction (where the other ends of the dissimilar metals are effectively rejoined) very accurately at a known constant, or compensable, temperature and 2. converting the highly nonlinear thermocouple response to a usefully linear function. These difficulties fortunately are very satisfactorily solved at present by electronic means.
There have remained, however, other serious difficulties and limitations in the thermocouple art stemming from the physical aspects of the manufactured junction. The two metals must, of course, be held in electrical contact with each other. When they are so held together by welding techniques, the manufacture is complex and often difficult or requires very special skills. Further the resulting junction may be brittle or otherwise weakened by the process; or it may be metallurgically changed by alloying or contamination by the welding materials or absorbed atmosphere. In addition, the welding matetial may "wick" or diffuse along the thermocouple materials thereby enlarging, displacing, or otherwise affecting the junction, all of these effects being aggravated by the necessity of working with metals having inherently dissimilar natures.
When the thermocouple is bonded by solder, it is temperature limited and relatively weak. And, again, a third metal is added to the metallurgically combination which may, in particular cases cause deleterious effects.
Most important, when an additional material is used to manufacture the junction, additional mass is added which inherently compromises the sensitivity and response speed of the junction.
It is, accordingly, an object of present invention to provide thermocouple apparatus which does not suffer the above and other limitations and disadvantages of the prior art.
It is another object to provide such apparatus which is very inexpensive, mechanically simple, and reliable, and which provides a rugged thermocouple of great strength and durability.
It is another object to provide such apparatus which incorporates no additional material at the junction and which in some embodiments utilizes no metallurgical bonding in the manufactured junction.
It is another object to provide such apparatus which is extremely sensitive and extremely low in thermocouple mass.